In our co-pending GB Application 03077237 (the ‘Prior Application’) there is described a ‘Positioning method and apparatus and a product thereof’. In its broadest method aspect the Prior Application provides a method of micro-machining, by means of a laser, a work piece comprising the steps of: locating the work piece on a carrier forming a part of a transport system whereby the carrier can be displaced along a path parallel to an X-axis of the work piece, a Y-axis lying transverse the path, and a Z-axis lying transverse the path; causing an output beam from the laser to establish a datum position relative to the X, Y and Z axis of a work piece and displacing the work piece along the path by way of the transport system so as to enable the work-piece to be subject to micro-machining process by way of the laser characterised by the steps of: maintaining distance between the datum position and a location on a surface of the work piece in the vicinity of the datum position; and accommodating local variations in thickness of the work piece so that the datum position is maintained at a fixed distance relative to a surface of the work piece.
The Prior Application goes on to formulate that the step of accommodating local variation in thickness in the work piece by displacing the datum position to follow the surface of the work piece. It goes on to envisage that the step of maintaining distance is undertaken by means of a distance sensing device comprising a body member riding on a fluid cushion on a first surface of the work piece the fluid cushion being established by a flow of fluid fed from the body member so as to maintain the body member at a predetermined distance from first surface; and in the event the body member is displaced from a current position of the body member due to a variation in thickness of the work piece any change in position of the body member perpendicular to the first surface is used to move the focussing or imaging lens to cause a corresponding change in the current datum position so as to restore the working datum position to its predetermined distance relative to the first surface of the work piece. Hereinafter such a device is referred to as being ‘of the type described’. Preferably the body member is located relative to a first side of the work piece and a further body member is provided located relative to a second side of the work piece on the opposite side of the work piece to the first side and the further body member serves to urge the work piece towards the body member when a local thickness of the work piece is reduced.
This concept of a distance sensing device comprising a body member riding over a surface of a work piece to be micro machined has now been developed further. Hereafter such a distance sensing device is referred to as a ‘puck’.